A headlight system includes a seat, a radiator, a mounting ring, a circuit board and a lens unit. A cooling device is connected to the back of the seat and includes a housing, a fan and an external cover. The housing has a receiving area in which the fan is located. The housing defines multiple first ventilation holes which communicate with the receiving area. The external cover is connected to the housing to seal the receiving area of the housing and has multiple second ventilation holes being opposite to the first ventilation holes of the housing. The fan sends out an air current to the radiator via the ventilation holes to quickly cool down the radiator.